1. Field of the Invention
The present invention relates to cameras and other imaging devices that utilize light sources to facilitate the operation of camera features. More particularly, the present invention relates to light sources used by camera subsystems such as automatic focusing systems, red-eye reduction systems, self-timers, etc. to perform their respective operations.
2. Description of the Related Art
Cameras that utilize automatic focussing subsystems and electronic flash devices are well known. For example, a camera that incorporates and utilizes an electronic flash device is shown and described in Japanese Examined Patent JP-B-49-19810, and in Japanese Laid-Open Patent JP-A-62-144123. A camera having an automatic focussing system and flash arrangement is further illustrated in a drawing figure that is attached hereto which has been identified as "FIG. 1."In FIG. 1, a camera 71 is shown in conjunction with an electronic flash device 72 which is mounted on camera 71 via a conventional "hot shoe" mounting system HS. In electronic flash device 72, a light emitting diode 73, a projection screen 74, and a projection lens 75 are arranged in a row facing a subject 80 which is to be imaged (e.g., a potted plant) by camera 71. Light emitting diode 73 is connected to a control circuit (not shown in the drawing) which is disposed in the electronic flash device 72. Light emitting diode 73 is used during automatic focussing operations prior to an actual imaging operation by camera 71 to ensure a proper focus state of an optical system of camera 71.
Normally, a focus detection unit 76 within camera 71 is used to facilitate automatic focussing (also referred to as "autofocus" or "AF") operations. Focus detection unit 76 utilizes a well-known divided-pupil phase-difference detection system and method to effect autofocus operations. In particular, the optical system in focus detection unit 76 causes a pair of images formed via a divided-pupil arrangement (not shown) to become incident on a light-receiving element array (not shown) in focus detection unit 76. In turn, the light-receiving element array photo-electrically converts the pair of optical images formed thereon into corresponding electrical signals. In turn, camera 71 detects an amount of displacement of a photographic lens from a desired/acceptable focus state by determining a phase difference between the photo-electric output signals generated by the light receiving element array. Such an automatic focussing system will be immediately apparent and understood by those skilled in the art.
Under abnormal conditions, such as when the contrast of a subject 80 is low, subject luminosity will be insufficient for focus detection unit 76 to accurately perform autofocus operations. As such, focus detection accuracy of focus detection unit 76 decreases. Accordingly, camera 71 can detect such a decrease in focus detection accuracy by determining decreased outputs of the light receiving element array. Accordingly, when camera 71 detects a decrease in focus detection accuracy, it may generate a light emission signal to cause light emitting diode 73 to illuminate.
Based on the aforementioned light emission signal, the light emitting diode 73 is caused to illuminate to produce additional light to aid in autofocus operations of focus detection unit 76. In turn, the light emitted by light emitting diode 73 passes through projection screen 74 and projection lens 75 to become incident on subject 80. The light generated by light emitting diode 73 that becomes incident on subject 80 is in the form of a projected pattern 81 which consists of light and dark stripes (as shown in FIG. 1). Focus detection unit 76 may perform autofocus operations based on projected pattern 81 with very high accuracy.
Although the generation of additional light by light emitting diode 73 will facilitate autofocus operations by focus detection unit 76 during poor lighting conditions, such additional light illuminates for about 0.3-1.0 seconds in the wavelength band of 660-700 nm. In situations where flash unit activation is not necessary (or not desired) to perform photographic operations, such additional light often unexpectedly enters and causes the eyes of a subject to close. As such, photographs are often ruined due to the emission of additional light which causes a subject's eyes to close or squint during imaging operations. Also, in circumstances in which the generation of such additional light is undesirable (e.g., when taking pictures at a play or live performance, etc.), a photographer often abandons AF type photography and elects to engage in manual focus adjustment as there is no way to prevent his camera from generating such additional AF illumination light. Depending on circumstances, manual focus adjustment can cause undesirable and lost images.
Thus, there exists a need to provide a new and improved apparatus and method for controlling a light source used in conjunction with an automatic focussing system. Such an apparatus must allow a light source to be controlled (e.g. turned off, dimmed, etc.) during otherwise poor lighting conditions to facilitate effective operation of an automatic focussing system. To be viable, such an apparatus must allow automatic focussing operations within an imaging device such as a camera to occur without impeding other imaging operations.